CHAPTER 8 - REACTIVITY TRENDS Flashcards
Why are group 2 elements known as reducing agents
They reduce other species
They are oxidised
eg. Ca —> Ca2+ + 2e-
What is formed when a redox reaction occurs between a metal and oxygen
Metal Hydroxide
eg. 2Mg + O2 –> 2MgO
What is formed when a redox reaction occurs between a metal and water
Metal Hydroxide + Hydrogen
eg. Sr + 2H2O –> Sr(OH)2 + H2
What is formed when a redox reaction occurs between a dilute acid and metal
Salt and Hydrogen
eg. Mg + 2HCl –> MgCl2 + H2
What are the solubility of Barium, Calcium, Magnesium and Strontium Hydroxides
Ba(OH)2 - Most soluble
Sr(OH)2
Ca(OH)2
Mg(OH)2 - Least soluble
Describe an experiment to show the trends in solubility of metal hydroxides
Add a spatula of each group 2 oxide to water in a test tube
Shake the mixture. On this scale, there is insufficient water to dissolve all of the metal hydroxide that forms. You will have a saturated solution of each metal hydroxide with some white solid undissolved at the bottom of the test-tube
Measure pH of each solution. The alkalinity will be sen to increase down the group
What are group 2 compounds used for in agriculture
Calcium Hydroxide added to fields as lime by farmers to increase pH of soils
Ca(OH)2 + 2H+ –> Ca2+ + 2H2O
What are group 2 compounds used for in medicine
Antacids to treat indigestion eg. Milk of magnesia or Calcium carbonates to neutralise stomach acids
Explain why group 2 elements are reducing agents
Group 2 metals add electrons to other species
Explain why the group 2 elements become more reactive down the group
Down group 2, the total energy from 1st and 2nd ionisation energies decreases because of increased atomic radius and increased shielding
It therefore becomes easier to remove the electrons and the reactivity increases
State and explain the trend in alkalinity of the solution formed when group 2 oxides are added to water
Group 2 oxides react with water forming the metal hydroxide.
Hydroxide ions in solution cause alkalinity.
Down group 2, the solubility of the metal hydroxide increases, increasing the pH and alkalinity
What is the name of Group 17 (7)
The halogens
Where to halogens occur
Stable halide ions, dissolved in sea water or combined with sodium or potassium deposits in salt mines
What colours and states do halogens form at RTP
Fluorine - Yellow Gas
Chlorine - Green Gas
Bromine - Red-Brown liquid
Iodine - Grey-black solid
Why are halogens known as oxidising agents
They cause oxidation in other species
causing themselves to be reduced
What is the trend of reactivity down the halogen group
It Decreases
What colours do Chlorine, bromine and iodine form in water
Cl - Pale green
Br - Orange
I - Brown
What colours do Chlorine, Bromine and Iodine form in cyclohexane
Cl - Pale green
Br - Orange
I - Violet
Why do halogens dissolve more readily into cyclohexane than water
Halogens and cyclohexanes are non-polar
Water is polar
What is the Displacement trend in halogens
Cl displaces Br and I
Br displaces I
I displaces nothing
(pg 113)
What is the displacement reaction of chlorine and sodium bromide
Cl2 + 2NaBr –> 2NaCl + Br2
What is a disproportionation reaction
A redox reaction in which the same element is both oxidised and reduced
What is chlorine used for
Water purification killing harmful bacteria
Cl2 + H2O –> HClO + HCl
How can a disproportionate reaction be seen
Adding indicator into a solution of chlorine and water
Turns red in the presence of HCl and disappears after the bleaching action of HClO (Chloric acid)
What is formed in the reaction of Cold, dilute NaOH (aq)
NaClO, NaCl and H2O
Disproportionation reaction
What is the test for Halide ions
Adding Aqueous silver ions, eg. Silver nitrate
State and explain the trend in boiling points of the halogens fluorine to iodine
Boiling point increases due to increasing electrons downgrade
This increases the strength of the London forces are more energy needed to break the intermolecular forces
What is the test for carbonate ions
Add Dilute nitric acid - effervescences
OR
Lime water test (Ca(OH)2) - goes cloudy
What is the test for Sulfate ions
Add Barium Chloride or barium nitrate
Will form BaSO4 - white ppt
SBC
What is the test for Halides
Add aqueous AgNO3 - forms 3 ppts of different colours, AgX
Add Aqueous NH3 - to test solubility
Cl - White ppt, Soluble Dilute NH3
Br - Cream ppt, soluble conc. NH3
I - Yellow ppt, Insoluble conc. NH3
HAgA
What is the correct order for Anion testing and why
1- Carbonate - no other test produces bubbles after this
2- Sulfate - forms white ppt, important to make sure it isn’t a carbonate which would look like a positive test if done after this due to the colour
3- Halide test, silver carbonate and silver sulfate will form precipitates insoluble in water
What is the test for ammonium
Add aqueous NaOH
Ammonia Gas will be produced - little bubbles formed as it is soluble with water
Mixture is warmed by reaction
Smell of ammonia and alkaline ammonia gas will turn damp pH paper blue
How could you distinguish between NaCl, NaBr and NaI by a simple test?
Add AgNO3 to aqueous solutions of each.
NaCl forms white ppt, dissolves In dilute NH3
NaBr forms cream ppt which dissolves in concentrated NH3
NaI forms yellow ppt, insoluble in conc NH3
Explain why it is important to carry out the carbonate test before carrying out the sulfate test on an unknown chemical
Dilute Nitric acid with carbonate ions, and no precipitate of barium carbonate will then form
Explain why if you are testing a mixture, it is important to use dilute nitric acid rather than sulphuric or hydrochloric for the carbonate test
If sulphuric acid is used, sulphate ions are added and will show up in the sulphate test
If hydrochloric acid is used, chloride ions are added, and will sharp in the halide test.
What is the purpose of a Barium meal
Coats inner lining of gut which will show up on x-ray - as it is insoluble (BaSO4 with water is taken)
Barium is usually toxic, but it doesn’t interact with the body due to BaSO4 being so insoluble
